Linear amplifier output stage correction circuit

Abstract

A linear amplifier with correction circuit is provided. According to one aspect, a linear amplifier includes a high current output stage configured to produce an output voltage and current to deliver power to a load. An output correction circuit receives the output voltage from the high current output stage and produces an error current proportional to a voltage drop across the high current output stage. An input stage receives at least one input and produces a first input current. A current-to-voltage resistor receives produces a first voltage that depends on the first input current and the error current. A first unity gain voltage buffer receives the first voltage from the current-to-voltage resistor and outputs a second voltage that is input to the high current output stage. The first voltage is compensated by the error current to reduce the voltage drop across the high current output stage.

What is claimed is: 
     
         1 . A linear amplifier for audio amplification, the linear amplifier comprising:
 an input stage configured to produce an output current proportional to a first differential input signal;   a current-to-voltage resistor in signal communication with the input stage, the current-to-voltage resistor configured to receive the output current from the input stage and convert the output current into an amplified signal voltage;   a first unity gain voltage buffer in signal communication with the current-to-voltage resistor, the first unity gain voltage buffer configured to receive the amplified signal voltage from the current-to-voltage resistor and produce a buffered amplified signal voltage;   a high current output stage in signal communication with the first unity gain voltage buffer, the high current output stage configured to receive the buffered amplified signal voltage from the first unity gain voltage buffer and to output a load voltage in response to the buffered amplified signal voltage, there being a first voltage drop across the high current output stage; and   an output correction circuit configured to receive, as a differential input voltage, the first voltage drop across the high current output stage, and to output an error current to the current-to-voltage resistor to compensate for the first voltage drop across the high current output stage.   
     
     
         2 . The linear amplifier of  claim 1 , wherein the output correction circuit includes a first operational transconductance amplifier configured to receive the first voltage drop across the high current output stage and to output the error current. 
     
     
         3 . The linear amplifier of  claim 2 , wherein the error current is equal to a transconductance of the first operational transconductance amplifier times the first voltage drop across the high current output stage. 
     
     
         4 . The linear amplifier of  claim 3 , wherein a transconductance of the operational transconductance amplifier is a reciprocal of a resistance of the current-to-voltage resistor. 
     
     
         5 . The linear amplifier of  claim 1 , wherein the output correction circuit includes:
 a second unity gain voltage buffer in signal communication with the first unity gain buffer, the second unity gain voltage buffer configured to receive the buffered amplified signal voltage;   an error current resistor configured to connect an output of the second unity gain voltage buffer to the output of the high current output stage, the error resistor having an error current proportional to the first voltage drop across the high current output stage; and   a current mirror in signal communication with the second unity gain voltage buffer, the current mirror configured to mirror the error current and output a mirrored error current to the current-to-voltage resistor.   
     
     
         6 . The linear amplifier of  claim 5 , wherein a resistance of the error current resistor is equal to a resistance of the current-to-voltage resistor. 
     
     
         7 . The linear amplifier of  claim 1 , further comprising feedback circuitry configured to connect the output of the high current output stage to provide a feedback current to the current-to-voltage resistor to compensate for nonlinearity in the input stage and to compensate for a second voltage drop across the first unity gain voltage buffer and the high current output stage. 
     
     
         8 . The linear amplifier of  claim 7 , wherein the feedback circuitry comprises a feedback resistor configured to develop a feedback current proportional to the load voltage, and a current conveyor configured to deliver the feedback current to the current-to-voltage resistor. 
     
     
         9 . The linear amplifier of  claim 8 , wherein a resistance of the error current resistor is equal to a resistance of the current-to-voltage resistor. 
     
     
         10 . The linear amplifier of  claim 1 , wherein the input stage includes a first operational transconductance amplifier. 
     
     
         11 . The linear amplifier of  claim 1 , wherein the input stage includes a differential current conveyor and the linear amplifier includes feedback circuitry configured to provide a feedback current from the output of the high current output stage to the differential current conveyor. 
     
     
         12 . The linear amplifier of  claim 7 , wherein the differential current conveyor has multiple inputs. 
     
     
         13 . A linear amplifier for audio amplification, the linear amplifier comprising:
 a high current output stage configured to produce an output current to deliver power to a load;   an output correction circuit in signal communication with the high current output stage, the output correction circuit configured to receive the output current from the high current output stage and produce an error current proportional to a voltage drop across the high current output stage;   an input stage configured to receive at least one input and produce a first input current;   a current-to-voltage resistor configured to receive the first input current and the error current and produce a first voltage that depends on the first input current and the error current; and   a first unity gain voltage buffer in signal communication with the input stage and configured to receive the first voltage from the current-to-voltage resistor and to output a second voltage that is input to the high current output stage, the first voltage being compensated by the error current to reduce the voltage drop across the high current output stage to zero.   
     
     
         14 . The linear amplifier of  claim 13 , wherein the output correction circuit includes a transconductance amplifier configured to receive the voltage drop across the high current output stage and output the error current. 
     
     
         15 . The linear amplifier of  claim 13 , wherein the output correction circuit includes:
 a second unity gain voltage buffer in signal communication with the first unity gain voltage buffer, the second unity gain voltage buffer configured to receive the second voltage from the first unity gain voltage buffer and output the error current; and   a current mirror in signal communication with the second unity gain voltage buffer, the current mirror configured to mirror the error current and output a mirrored error current to the current-to-voltage resistor and to the first unity gain buffer.   
     
     
         16 . The linear amplifier of  claim 15 , further comprising an error current resistor configured to connect an output of the second unity gain buffer to the output of the high current output stage and wherein the second unity gain buffer is configured to provide the error current to the error current resistor. 
     
     
         17 . A linear amplifier for audio amplification, the linear amplifier including an input stage, followed by a first unity gain buffer, followed by a high current output stage configured to deliver power to a load, the linear amplifier further comprising an output correction circuit, the output correction circuit comprising:
 a second unity gain buffer in signal communication with the first unity gain buffer, the second unity gain buffer configured to receive an output of the first unity gain buffer and to deliver an error current; and   a current mirror in signal communication with the second unity gain buffer, the current mirror configured to mirror the error current and deliver the mirrored error current to an input of the first unity gain buffer to compensate for a voltage drop across the high current output stage.   
     
     
         18 . The linear amplifier of  claim 17 , further comprising an error current resistor in signal communication with an output of the high current output stage, the error current resistor configured to provide an error current proportional to the error voltage. 
     
     
         19 . The linear amplifier of  claim 18 , wherein a resistance of the error current resistor is equal to a resistance of a current-to-voltage resistor configured to convert an output current of the input stage to an input voltage to the first unity gain buffer. 
     
     
         20 . The linear amplifier of  claim 19 , wherein the error current is added to the output current of the input stage.